Isoprene prepared by the catalytic dehydration of 2-methyl-2,3-butanediol

ABSTRACT

1. A PROCESS FOR THE DEHYDRATION OF 2-METHYL-2,3BUTANEDIOL CONSISTING ESSENTIALLY OF CONTACTING 2-METHYL2,3-BUTANEDIOL IN THE VAPOR PHASE WITH A CATALYST AT A TEMPERATURE IN THE RANGE OF 200 TO 500* C., SAID CATALYST BEING THORIUM OXIDE AND LITHIUM PHOSPHATE IN WHICH THE LITHIUM PHOSPHATE HAS A SUBSTANTIALLY NEUTRAL PH AND WHEREIN THE THORIUM OXIDE AND LITHIUM PHOSPHATE ARE MAINTAINED SEPARATE AND DISTINCT FROM EACH OTHER, IN DISCRETE BEDS, SAID 2-METHYL-2,3-BUTANEDIOL CONTACTING SAID THORIUM OXIDE BED FIRST AND THEN SUBSEQUENTLY CONTACTING SAID LITHIUM PHOSPHATE.

United States Patent 3,849,512 ISOPRENE PREPARED BY THE CATALYTIC DEHY- DRATION 0F 2-METHYL-2,3-BUTANEDIOL William G. Bowman, Pasadena, Tex., assignor to Petro- Tex Chemical Corporation, Houston, Tex. No Drawing. Filed Dec. 10, 1970, Ser. No. 96,975 Int. Cl. C07c 1/24 US. Cl. 260-681 Claims ABSTRACT OF THE DISCLOSURE Neutral Li PO is used to dehydrate 2-methyl-2,3-butanediol in a vapor phase process at about 375 to 425 C. by passing the diol vapors through a fixed bed of the catalyst to produce high yields of isoprene and isoprene precursors. The Li PO can be employed with ThO to give some improvement in the process. The two components are maintained in separate beds.

The present invention relates to a process for the dehydration of 2-methyl-2,3-butanediol to produce isoprene. More particularly the invention relates to the use of a lithium phosphate catalyst.

Natural rubber is a polymer of 2-methylbutadiene (isoprene). Natural rubber is a polymer in which the isoprene units are linked in the 1,4 manner and the groups on the double bond have cis configuration. In the early years of synthetic rubber development, great difiiculty was experienced in duplicating the natural rubber configuration and styrene-butadiene-rubber came to fore dominating synthetic rubber production. Now catalysts and processes have been developed for producing superior synthetic polyisoprene, substantially duplicating natural rubber.

The expectations were that synthetic polyisoprene would displace SBR since it is a generally superior and more desirable synthetic rubber than SBR. However, isoprene availability became a problem. Numerous methods of isoprene production have been proposed, e.g., the pyrolysis of terpene hydrocarbons, dehydrogenation of isopentane isopentene, catalytic pyrolysis of ethylenically unsaturated ether, synthesis and dehydration of dimethyl vinylcarbinol and dehydration of 2-methyl-2,3-butancdiol.

Each method has substantially deficiencies, for example, dehydrogenation of isopentane, or isopentene is subject to a rather non-selective reaction with the present state of the art.

The dehydration of 2-methyl-2,3-butanediol has always been considered unattractive because of the difliculty of producing the diol, however, recent technological advances in this area have entirely reversed this situation and the production of 2-methyl-2,3-butanediol in large economical quantities is possible.

It has now been found that 2-methyl-2,3-butanediol can be converted to isoprene in good yields by using a substantially neutral lithium phosphate catalyst.

The process is vapor phase carried out at temperatures in the range of 200 to 500 C., preferably around 350 to 450 C. and usually in the range of about 375 to 425 C. The process is generally carried out at atmospheric pressure but may be practiced at either sub or super atmospheric pressures. The 2-methyl-2,3-butanediol is passed through a reactor containing a Li PO catalyst. Usually the vaporous diol feed is mixed with a vaporous or gaseous diluents. Suitable diluent includes helium, nitrogen, argon, other inert gases, hydrogen, steam or mixtures thereof. The diluent is usually present in an amount of about 0.5 to 20 moles per mole of diol and more generally about 1 to 10 moles per mole of diol.

The contact time of the feed with the catalyst is about 1 to 6 seconds. Since the process is carried out by passing a vaporous feed through the catalyst bed it is convenient to express the contact time by means of the flow rate in terms of liquid volume of diol to be dehydrated per volume of dehydration zone containing catalyst per hour (referred to as LHSV). The optimum flow rates will be dependent upon such variables as temperature of the reaction, presure, particle size and so forth. Usually, the LHSV will be between .5 and about 4. For calculation, the volume of a fixed bed dehydration zone containing catalyst is that original void volume of reactor space containing catalyst.

The Li PO catalyst can be prepared by reacting lithium hydroxide and phosphoric acid. The resulting salt can be adequately washed to provide a catalyst which is substantially neutral, i.e., pH of approximately 7.2 or the pH can be adjusted during the precipitation. It has been found that neither basic or acid Li PO are nearly as suitable as neutral salt.

In a particular embodiment it has been found that a bed of Li PO combined with a bed of thorium oxide (thoria) produces an enhanced effect. The catalysts are maintained in separate beds. The order of the beds is not critical although the use of Li PO as the final bed seems to offer some advantage. The ratio of catalyst surface of Li PO, to Th0; is about 10:1 to 1:10 and more preferably about 3:1 to 1:2.

The catalysts may be pelleted and used as such or may be deposited on or in carriers such as pumice, graphite, silica, alumina, silica-alumina, fullers earth, firebrick and the like. The carriers should be neither basic nor strongly acidic.

The catalyst can be employed in a fixed or moving bed such as a fluidized bed. In the case of a two component system the various catalyst beds should be kept separate. Ordinary and conventional equipment and techniques used for dehydrations or dehydrogentations can be used for this process. Those skilled in the area of process design will readily be able to select suitable equipment.

The following examples will illustrate the invention as described above. Conversions, selectivities and yields are inmole percent, all other percentages are by weight unless specified otherwise.

The runs were made in a downflow Vycor 750 x 25 mm. O.D. reactor heated with an electric furnace. Vycor Rachig (6 x 6 mm.) rings were placed above and below the catalyst bed to preheat feed and position the catalyst. Gas chromatography was used to identify the products by the internal standard method using pentene-l.

EXAMPLES Catalyst Preparation Li PO .-To 50 mls. of the carrier was added 2.90 g. of Li'OH.H O dissolved in 50 mls. of H 0. H PO was added to pH 6.5. LiOHH O was added to pH 7.2. The slurry was evaporated with agitation in a Vycor dish.

ThO .-100 g. of T11(NO3)4 4H O was dissolved in 3.5 liters of hot H O. 12.6 g. of oxalic acid plus 50 mls. of H50 in 500 mls. of H 0 were slowly added to the Th(NO solution. The precipitate was washed 8 times by decanting and adding additional H O. The residue was filtered and heated to 375 C. overnight. The cake was broken up carefully and screened to x A1" size.

Li HPO .14.75 g. of LiOH.-H O was dissolved in mls. of H 0 and mixed with 57.4 g. (50 mls.) AMC carrier in Vycor disk. 20.9 g. of H PO was then added. The resulting slurry was dried with constant stirring.

LiH P0 .4ame as above except as follows: LiOH.H O 7.37 g. H POR 20.29 g. of 85%. AMC carrier 57.4 g. (50 mls.).

3 The Process In each of these examples 50 ml. of catalyst was employed in the described reactor. The feed was 2-methyl- 2,3-butanediol diluted with 10% H O (mole ratio wherein the thorium oxide and lithium phosphate are maintained separate and distinct from each other, in discrete beds, said 2-methyl-2,3-butanediol contacting said thorium oxide bed first and then subsequently contacting 5 p p y 2. The process according to claim 1 wherein the tem- (catalyst support materials 1n Examples 17 to 20) and th f 3 50 t 4500 C the other conditions of the run as well as the results. Each perature m 6 range run was approximately 14 to 30 minutes in duration de- The Process according 10 61111111 2 wherein the pending on the rate at which the diol was fed. 10 p rat re 1s m he r g f 375 to 475 C.

TABLE Dehydration catalysts results Product yield, mole percent Percent selectiv- Contact Gas- Tem- Methyl ity to Diols time, eous pera- Percent 3-methy1- 3-1nethy1- iscisoprene fed, secdilture, con- Iso- 2,3-butan- 3 buteneropyl and pre- Ex. Catalyst composition moles 0nd LHSV uent 0. version prene OXldB 2-01 etone cursors 1 LiaPO4 on 6 x 6 mm. Vycor 0.26 2. 2 H; 425 98. 63. 8 4. 5 7. 2 22. 4 76. 6

Raschig Rings. do 0. 25 2. 2 2. 3 H; 425 92. 2 44.1 4. 4 12. 2 19. 8 65.8 0.25 2. 2 2. 2 H1 390 98. 4 1. 5 2.0 72. 5 11.4 77. 2 0.25 2. 2 2. 2 He 425 99. 0 48. 2 11.3 6.1 25. 2 65. 6 0. 25 2. 2 2. 2 H, 425 99. 0 22. 5 19. 0 1.0 53.0 42. 5 6 LiaPO4 FMC on AMC 0.25 2. 2 2. 2 He 425 42. 7 2.0 10. 6 8.2 17. 7 48. 7 7 LiaPO4 on AMC 5 0.42 2. 4 2. 3 H 425 99. 0 51. 9 12.0 6. 6 21. 7 70. 5 8- LlzHPO on AMC. 0.252 2.2 2.2 H, 425 88.0 5.9 1. 6 9. 1 10.3 43.7 9. LiHzPO4 on AMC 5 0. 256 2. 2 2. 2 H1 425 91.0 21. 9 7. 7 11. 3 45.0 44. 9 10 L110 on AMC 6 0.26 2. 2 2. 2 He 425 36. 3 0.73 7. 1 4. 2 5. 4 33.1 11 Lithium bromide on AMC 6 0.26 2. 2 2. 2 He 425 76. 6 2. 2 1. 0 9. 2 52. 8 15. 0 12 Tl101-50 mls, LlaPO on 0.26 4. 4 1.1 H, 425 99. 0 51. 4 3. 3 3. 7 23. 9 58. 4

BS131-50 mlsJ. 13 do. 0.42 4. 4 1. 1 H, 425 99. 0 64. 8 3.8 7. 0 14. 8 74. 8 14 4 0. 42 4. 4 1. 1 H; 425 99. 0 38. 4 6.3 16. 9 21. 1 61. 6 15 d0. 0.42 4. 4 1.1 Hz 425 99. 0 55. 5 6. 4 8. 9 19. 9 70.8 16 Same a3 12 but intimate 0.42 4. 4 l. 1 H) 425 99. 0 28. 7 11.8 4. 9 45.2 45. 4

mixe e 17 Vycor Raschig R. 6 x 6 mm 0. 26 2. 4 2. 2 H] 425 13.0 0. 1 1.0 0.1 2.0 8.5 18 Quartz chips 0. 26 2. 4 2. 2 H, 425 11. 0 0.5 0. 1 0. 6 0. 1 10. 9 19 B8131, silica 0. 26 2. 4 2. 2 H, 425 99. 0 15. 6 0. 1 01 71. 1 15.6 AMC 5 l 0.26 2.4 2. 2 H, 425 98. 5 10. 1 24. 1 3. 1 53. 2 37. 9

1 Second run, same catalyst, no regeneration.

1 H01 leached and calcined at 700 C.

3 H01 leached, dried, but not calcined.

4 LlaP04 obtained from FMO Corp. pH was about 8.0. Untreated AMC 7/9 mesh.

Referring to the Table it should be noted that since isoprene is the desired product a high yield of isoprene indicates a preferred system, however, note also that a high selectivity to isoprene and isoprene precursors even in the face of low isoprene yields indicate a suitable process since the precursors can be separated from the isoprene and recycled to the process. Examples 1 and 2 represent a preferred system. Example 4 also is a preferred system, whereas Examples 5 and 6 represent non-neutral systems in that thesupport in Example 5 was leached with HCl but not calcined (leaving a strongly acid system) and the Li PO of Example 6 was alkaline (pH 8.0). Example 7 however, represents a neutral LiPO system and gives excellent overall results. Example 3 shows that ThO alone performs poorly in regard to the yield of isoprene and would require a great deal of recycling to obtain suitable production.

Examples 8 and 9 show the relatively poor results with lithium acid phosphates. Examples 10 and 11 show the use of other lithium compounds to be totally unsuitable.

Examples 12-15 show the use of two beds of catalyst (ThO and Li PO in 4 continuous runs. There is a drop in the effectiveness of the catalyst in the third continuous run (Example 14) which is substantially overcome by regenerating the catalyst (burning off coke) with air at 550 C. for 120 minutes, prior to the fourth run (Example 15) Example 16 shows the same catalyst system but with the two components intermingled. The results are relatively poorer.

Examples 17-20 demonstrate the eifect of some supports alone.

The invention claimed is:

1. A process for the dehydration of 2-methyl-2,3- butanediol consisting essentially of contacting 2-methyl- 2,3-butanediol in the vapor phase with a catalyst at a temperature in the range of 200 to 500 C., said catalyst being thorium oxide and lithium phosphate in which the lithium phosphate has a substantially neutral pH and Four consecutive runs; same catalyst charge prior to fourth run (Example 15) catalyst regenerated at 550 C. in air [or minutes.

7 Two layers, Th0; contacted the diol first.

B Low surface area silica.

9 Low surface area alumina-silica.

4. The process according to claim 2 wherein said 2-methyl-2,3-butanediol contacting said catalyst contains a vaporous, inert diluent in a mole ratio of diluent to 2-methyl-2,3-butanediol of about 0.5:1 to 20:1.

5. The process accordin to claim 4 wherein the mole ratio of diluent to diol is about 1:1 to 10: 1.

6. The process according to claim 2 wherein the ratio of surface of Li PO to ThO is about 10:1 to 1:10.

'7. The process according to claim 2 wherein the Li PO is deposited on a carrier selected from the group consisting of pumice, graphite, silica, alumina, silicatealumina, fullers earth and firebrick.

8. The process according to claim 7 wherein a vaporous diluent is present in a mole ratio of diluent to diol of about 1:1 to 10:1.

9. The process according to claim 6 wherein the temperature is in the range of 350 to 450 C., and a vaporous diluent is present in a mole ratio of diluent to diol of about 1:1 to 10:1.

10. The process according to claim 9 wherein the Li PO is deposited on a carrier selected from the group consisting of pumice, graphite, silica, alumina, silicaalumina, fullers earth and firebrick.

References Cited UNITED STATES PATENTS 3,758,612 9/ 1973 Maurin 260681 3,647,903 3/1972 Maurin 260-681 3,510,537 5/1970 Sheng et a1. 260-681 3,391,213 7/1968 Fetterly 260-681 2,986,585 5/1961 Denton 260-681 1,923,569 8/1933 Mueller-Cunradi 260-681 1,944,153 1/1934 Mueller-Cuuradi 260-681 2,204,157 6/1940 Semon 260681 DELBERT E. GANTZ, Primary Examiner VERONICA OKEEFE, Assistant Examiner g gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Page n 9, 512 Dated November 19, 1974 Invgntmflg) William G. Bowman It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col; 2, line 7 reads "presure" should read pressure C01. 3, Example 6 reads "AMC but should read AMC Col. 3, Example 20 reads "AMC "'but should read AMC Signed and sealed this 3th day of April 1975.

(SEAL) Attest:

C MARSHA LL DANE? Commissioner of Patents and Trademarks RUTH C. I-IASOII Attesting Officer 

1. A PROCESS FOR THE DEHYDRATION OF 2-METHYL-2,3BUTANEDIOL CONSISTING ESSENTIALLY OF CONTACTING 2-METHYL2,3-BUTANEDIOL IN THE VAPOR PHASE WITH A CATALYST AT A TEMPERATURE IN THE RANGE OF 200 TO 500* C., SAID CATALYST BEING THORIUM OXIDE AND LITHIUM PHOSPHATE IN WHICH THE LITHIUM PHOSPHATE HAS A SUBSTANTIALLY NEUTRAL PH AND WHEREIN THE THORIUM OXIDE AND LITHIUM PHOSPHATE ARE MAINTAINED SEPARATE AND DISTINCT FROM EACH OTHER, IN DISCRETE BEDS, SAID 2-METHYL-2,3-BUTANEDIOL CONTACTING SAID THORIUM OXIDE BED FIRST AND THEN SUBSEQUENTLY CONTACTING SAID LITHIUM PHOSPHATE. 